I'm trying to clarify something. If I say: 'Davus sacculum in mensa ponit.' 'Mensa' here is ablative - the thing on which the bag is put. So far so good. But in Orberg's LLPSI Ch 9 he has something like Pastor ovem in umeros imponit'. Now I suppose it seems sensible that umeros is accusative plural.....but can anyone clarify the rule here? Is it because he has taken the sheep on his own shoulders. Is it that 'imponit' takes its object in the accusative? Is it something to do with imponit denoting motion towards? I'm looking at the word 'in' and expecting ablative. Thanks for any views..

According to L&S "aliquam rem in aliquâ re ponere" and "aliquam rem in aliquam rem imponere" are more usually said, but you can say (more rarely): "aliquam rem in aliquâ re imponere" et "aliquam rem in aliquam rem ponere".

Sometimes verbs follow different rules when they have prefixes attached. That's usually not the case when the prefixed verb has the same essential meaning (e.g. "venīre" and "advenīre"), but as we see here with "imponere", there can be exceptions.

There's a chapter in Wheelock that is about, among other things, how some verbs take the dative instead of the accusative when prefixed (but, again, this is usually when the verb changes its essential meaning). For example, "sequor eum" (I follow him) but "obsequor eī" (I obey him). So be ready for those when you run into them...

I've had a look at Allan & Greenough's "New Latin Grammar". They have the following to say about this matter.

430. Verbs of placing, though implying motion, take the construction of the place where:Such are pono, loco, colloco, statuo, constituo, etc.:

- qui in sede ac domo collocavit (Par. 25), who put [one] into his place and home.- statuitur eques Romanus in Aproni convivio (Verr. iii. 62), a Roman knight is brought into a banquet of Apronius.- insula Delos in Aegaeo mari posita (Manil. 55), the island of Delos, situated in the Aegean Sea.- si in uno Pompeio omnia poneretis (id. 59), if you made everything depend on Pompey alone.

NOTE.--Compounds of pono take various constructions (see the Lexicon under each word).

So let's have a look at a dictionary, in this case the "Latin-English Dictionary For The Use Of Junior Students" (1904, John T. White), and its definition of "impono". It gives (among many other uses) the following example for "impono":

Indeed, but consider the direction of change in the later edition and the reasons for it (which we can only speculate about, I guess).Ut dicis, at intuere naturam emendationis in editione noviore et quâre ea faciatur (quod pro certo gnoscere non possumus, ut conjecto).